Fabrication And Properties Of One-Dimensional Nano-Material/Rubber-Based Microwave Absorbing Composites

With X-band(8.2-12.4 GHz)frequency electromagnetic wave being extensively utilized in wireless network,satellite communications and radar technology,adverse effects caused by electromagnetic radiations on human health and communication security are becoming severe problem worldwide.Typical characteristics of ideal microwave absorbing materials include lightweight,strong absorption and wide effective absorption band(EAB).In the design of rubber-based microwave absorbing composites,the immisicle rubber can induce the selective distribution of fillers in the matrix and improve the filling efficiency.The absorbing fillers with one-dimensional nanostructure is easier to form a well-established electromagnetic loss network inside the composites due to its higher aspect ratio.In this thesis,three one-dimensional nano-materials filled rubber microwave absorbing composites were fabricated with natural rubber(NR)and nitrile butadiene rubber(NBR)blends.The main results are as follows:MWCNT/NR/NBR(50/50)microwave absorbing composites were fabricated using MWCNT as absorbing fillers and NR/NBR(50/50)blend as matrice.The effects of MWCNT content on the micromorphology,microwave absorbing performance and mechanical properties of composites were investigated.The micromorphology of MWCNT/NR/NBR(50/50)composites was correlated with the filling content of MWCNT.The content of MWCNT affected the distribution preference in the NR/NBR blends and the phase domain size of the blend.When the filling content was 3 phr,MWCNT were mainly distributed in the NR phase.As the content of MWCNT increased from 6 phr to 12 phr,the phase domain size of the blend decreased,and MWCNT gradually mirgrated from NR phase to the NR/NBR interface.With the increase of MWCNT filling content,microwave absorbing performance of the composites was enhanced first and then weakened.When the filling content of MWCNT,the composite had a better microwave absorbing performance.The minimum reflection loss RLmin of the composite can reach to-20.96 dB at 11.5 GHz with matching thickness of 5.2 mm and the corresponding EAB reached 1.1 GHz.Influenced by the micromorphology,the composite filled with 9 phr MWCNT showed the maximum elongation at break and tensile strength of this composite wasup to 14.9 MPa.PPyNTs with several micrometers in length,104.2±18.4 nm in diameter,31.4±3.4 nm in wall thickness and 0.35 S/cm in conductivity were prepared by a reactive selfdegraded template method,and PPyNT/NR/NBR composites were fabricated using PPyNT as absorbing fillers.In order to obtain excellent microwave absorbing performance and mechanical properties of the composites,the content of PPyNT and the blending ratio of NR/NBR were optimized to to explore the optimal formulation.The micromorphology of the composites showed that the content of PPyNT and the NR/NBR blending ratio had little effect on the distribution prepference of PPyNT in the NR/NBR blends.The results showed that the 6 phr PPyNT filled NR/NBR(90/10)composite had superior microwave absorbing performance and mechanical properties.The composite had an RLmin of-56.67 dB at 2.9 mm and corresponding EAB of 3.7 GHz,covering 86%of the X-band(8.2-12.4 GHz).At the same time,the composite also had low Payne effect,good dispersion effect,excellent mechanical properties.Its tensile strength was up to 10.3 MPa and elongation at break was 488%.Carbonized polypyrrole nanotubes(C-PPyNT)with 89.19 ± 18.77 nm in diameter,20.15 ± 3.22 nm in wall thickness and 0.023 S/cm in conductivity were successfully prepared by using PPyNT as a precursor,and C-PPyNT/NR/NBR(50/50)composites were fabricated using C-PPyNT as absorbing fillers.The effect of filling content of CPPyNT on the micromorphology,microwave absorbing performance and mechanical properties of the composites was investigated preliminarily.The distribution of CPPyNT in NR/NBR(50/50)blend was affected by its content.When the filling content was 3 phr,C-PPyNT mainly distributed in NR phase.With the increase of C-PPyNT content,it migrated gradually to the NR/NBR interface.With the increase of the content of C-PPyNT,the microwave absorbing performance firstly increased and then decreased.The RLmin and EAB of the composite filled with 6 phr C-PPyNT were-33.68 dB and 1.3 GHz respectively at 8.2 mm.The tensile strength of the composite was 10.5 MPa,which was 88.13%higher than that of the composite filled with the same content of PPyNT.